Leather-coating composition



United States Patent Orifice a My 19.,

season 2 Claims. (Cl. zen-32.8

This invention relates to a novel composition of matter used to coat theleather element in shaft and rod seals. This application is a divisionof our application Serial No. 713,024, filed February 3, 1958, now U.S.Patent No. 2,983,131, which in turn is a division of our applicationSerial Number 540,104, filed October 12, 1955, now U.S. Patent No.2,854,267, which was a continuation-in-part of our application SerialNumber 519,862, filed July 5, 1955 now abandoned.

Leather has long been favored as far superior to most materials as apliant sealing element for shafts, reciprocating rods and the like.Despite this, it is recognized that leather has certain disadvantagesand fails to exhibit, to the degree desired, all the characteristicsneeded to meet the ever increasing requirements for a satisfactory seal.For example, leather varies Widely in density, resilience, porosity andflexibility, all of which affect performance and suitability for use assealing elements. Accordingly, over the years much effort has beendirected toward improved processing procedures in an endeavor to providea product of more uniform properties and longer service life. Inaddition, these attempts have included the augmentation of existingproperties as well as the inclusion of new ones.

Another facet of the problem derives from the fact that certain desiredproperties of leather are customarily found only in combination withundesirable ones. For example, a leather having the desired flexibilityis too soft to maintain good sealing contact with an eccentricallyrotating shaft, or one which vibrates or whips as it rotates. Also, aflexible leather usually is quite porous. In consequence, it has a highreservoir capacity for lubricantan advantageous quality. But thisporosity is also attended by seepage of lubricant through the side Wallsof 'the leathera highly undesirable quality. Previous efforts to sealthe pores have destroyed the leathers capacity for storing lubricant andhave stiffened the leather vobjectionably.

of novel coating compositions suitable for sealing the surface ofleather, textiles and the like and of imparting new and uniqueproperties thereto in a simple, inexpensive and highly eflicient manner.

Numerous other objects and. advantages of the invention will becomereadily apparent from the following detailed specification.

The invention provides a thin film or veneer of a special elastomerbonded to one or more surfaces of the leather. If. only one surface ofthe leather member is to be coated, it is preferable to coat the hairside rather than the opposite flesh side and, in a shaft seal, to somount the seal in the housing bore that the elastomeric veneer is incontact with the shaft and is remote from the interior of the housing.

The principal functional ingredients of the veneer are a syntheticoil-resistant elastomer such as neoprene, a polyacrylic, a nitrile, or achlorosulfonated polyethylene rubber having a suitable dry lubricantdispersed therein, such as graphite, molybdenum disulfide, mica or talc.These substances, compounded along with a suitable solvent vehicle in amanner to be disclosed below, are applied in liquid form to the surfaceof the leather sealing member and then vulcanized.

The elastomer does not penetrate beyond the base of the hair poreopenings or of the surface crevices and other imperfections of theleather. This confinement of the veneer to the immediate surface area ofthe leather and its absence from the many voids in the body of theleather is highly important and has several advantages. Thus, theabsence of elastomer from the interior body of the leather permits of afree and natural capillary flow of lubricant within the leather in apath generally parallel to the inner and outer surfaces. Secondly, themany voids naturally present in the leather are available as lubricantstorage reservoirs. And, thirdly, the inherent flexibility of the bodyof the leather is not adversely affected by the presence ofincompressible particles filling the voids. And, of specialsignificance, the exterior surface of the leather or the one in contactwith the rotating shaft is sealed by a thin film of resilient materialwhich is highly resistant to attack by lubricants, relatively imperviousto both liquids and gases, and has a coefficient of friction at least50% lower than the identical leather sealing element without the surfacecoating of this invention.

In practice, a film thickness of 2 to 5 mils has been found mosteffective. Greater thicknesses can be employed but have a tendency tostiffen the leather objectionably and are not found to add to theservice life of the sealing element to any material extent.

Coating both sides of the sealing element has certain advantages. Itstiflens each side of the leather in equal degree; it provides a smoothfinished surface on both sides of the sealing element; and it provides asubstantially 'sealed reservoir for lubricant within the body ofleatherproper. The outer rim of this reservoir is sealed by thesurrounding housing for the sealing element, leaving only the innerperipheral edge exposed to the interior of the appliance housing and thesupply of oil therein. If the seal is to be used in a location notexposed to lubricating mediums, then the sealing element can besaturated with lubricant before installation. Thus, in either mode ofuse, the sealing edge of the lip has a continuous supply of oilavailable at all As soon as a film of oil between the shaft and thecontacting edge of the seal tends to disappear, it is immediatelyreplenished from the supply stored by capillary action in the body ofthe seal. Furthermore, the low friction coating in direct contact withthe shaft contains a dry lubricant locked within the coating. This drylubricant supplements the liquid lubricant within the body of thesealing element.

The coating compositions which we have found to be so satisfactory forsurface films or coatings are elastomers or rubber-like syntheticsincorporating one or more dry lubricants that are dispersed therein toimpart lubricity and other related properties important to a properlyfunctioning seal. For example, the coating elastomer may be Neoprene GN.(trade name for neoprene with an antioxidant stabilizer), or Neoprene,GRT (trade name for neoprene with low temperature crystallizationinhibitor), standard elastomen'c polymers of chloroprene commeroiallyavailable from E. I. du 'POl'llt dc Nemburs & 00. One hundred parts ofthis material should be compounded for rapid curing and mixed withbetween and 60 parts by volume of a filling agent having lubricatingproperties such as graphite, molybdenum disulfide, mica or talc. F orgraphite, the range by weight is between and 120 parts per 100 partselastomer.) This mixture is dissolved in a suitable solvent to provide alow viscosity solution of 5-20% solids. If a lower solids content isemployed, the film does not distribute uniformly to provide a reliablycontinuous veneer, while a solution of higher solids content is tooviscous for satisfactory results. It will, of course, be understood bythose skilled in the handling of elastomeric compositions that suitablecuring agents, anti-oxidants and accelerators are required as usual.

Suitable solvents include a mixture of one or more aromatics (toluene,benzene, or xylene and homologues of them) with paraffin hydrocarbons(e.g., gasoline or kerosene) or ketones (acetone, methyl-ethyl-ketone,and other liquids of the group) or naphthas. Wide variations ofquantities can be used, and which solvent mixture is selected willdepend on factors such as evaporation rate desired, cost, toxicity, etc.

The following specific examples sufiice to illustrate the relativeproportions of constituents which have been found particularly suitablein actual practice:

EXAMPLE I Neoprene rubber Another composition giving excellent resultsemploys copolymers of butyl acrylate and acrylonitrile or ethyl acrylateand chloroethyl-vinyl ether in lieu of neoprene. Such a composition maybe compounded as follows:

EXAMPLE II Polyacrylic elastomer Constituents: Parts by weightLactoprene BA 12.5 (An acrylonitrile (87.5 )-butyl acrylate (12.5%copolymer) 100 Stearic acid 1 Sulfur 1 Triethylene tetramine 4 Graphite80 Total solids 186 Methyl-ethyl-ketone 1,504 Toluene 170 Total liquids1,674

Grand total 1,860

Still another composition which we have found to provide an excellentadherent veneer for leather employs chlorosulphonated polyethylene as aprincipal elastomeric component. This coating composition is made fromthe Kenflex BKenrich Corp. trademark for a non-volatile syntheticpolymer of aromatic hydrocarbons which has a melting point of 80 F Inany of these examples, mica, talc, and molybdenum disulfide may besubstituted for graphite, in equal volumes.

Graphite is, however, preferred.

Any of the foregoing compositions may be applied to the leather bydipping, dripping, spraying or other common coating techniques. Curingor molding may be for one minute at a temperature of approximately 275F. It will, of course, be appreciated that the pressure, molding periodand temperature may be varied over a considerable range as found to givethe best results for the particular leather and coating compositionbeing used. Molding may be carried out for longer periods (up to 90seconds) at lower temperatures, and shorter periods (down to 10 seconds)at higher temperatures, but temperatures higher than 325 F. should beavoided, else damage to the leather may result.

We claim:

1. A coating composition for leather liquid-lubricantsealing members,consisting essentially of a solvent-elastomer dispersion of (1) 8095% byweight of a solvent mixture consisting (A) an aromatic solvent selectedfrom the group consisting of benzene, toluene and xylene, and (B) analiphatic solvent selected from the group consisting of acetone, methylethyl ketone, gasoline, kerosene and naphtha, and

(2) 520% by weight of a solids mixture consisting essentially of '(C)liquid-lubricant-resistant flexible elastomer selected from the groupconsisting of polychloroprene, copolymers of ethyl acrylate andchloroethyl vinyl ether, copolymers of butyl acrylate and acrylonitrile,and chlorosulfonated polyethylene, and (D) 10-60 parts by volume per 100parts by volume of (C) of a dry lubricant selected from the groupconsisting of graphite, molybdenum disulfide, talc, and mica.

2. A coating composition for leather liquid-lubricantsealing members,consisting essentially of a solvent-elastomer dispersion of (1) -95% byweight of a solvent mixture consisting (A) about by weight of (1) ofmethyl ethyl ketone 75 (B) about 10% by weight of 1) of toluene 5 (2)5-20% by weight of a solids mixture consisting essentially of (C) aliquid-lubricant-resistant flexible elastomer selected from the groupconsisting of polychloroprene, copolymers of ethyl acrylate andohloroethyl vinyl ether, copolymers of butyl acrylate and acrylonitrile,and chlorosulfonated polyethylene, and (B) 10-60 parts by volume per 100parts by volume of (C) of a dry lubricant selected from the groupconsisting of graphite, molybdenum disulfide, talc, and mica.

References Cited in the file of this patent UNITED STATES PATENTSStewart Nov. 16, 1937 Dombnow et a1 Mar. 22, 1949 Pyle June 10, 1952Cheronis Apr. 14, 1953 Wilson Sept. 30, 1958 Crissey et a1 Apr. 216,1960 Morris May 31, 1960

1. A COATING COMPOSITION FOR LEATHER LIQUID-LUBRICANTSEALING MEMBERS,CONSISTING ESSENTIALLY OF A SOLVENT-ELASTOMER DISPERSION OF (1) 80-95%BY WEIGHT OF A SOLVENT MIXTURE CONSISTING OF